Electrically-operated heatgenerating devices



United States Patent ELECTRICALLY-OPERATED HEAT- GENERATING DEVICESLouis B. Pendleton, St. Louis, Mo. Application July 21, 1954, Serial No.444,735 Claims. (Cl. 219-19) This invention relates to improvements inelectricallyoperated heat-generating devices. More particularly thisinvention relates to electrically-operated heat-generating devices whichcan be releasably placed within a structure to heat the area within thatstructure.

It is therefore an object of the present invention to provide animproved electrically-operated heat-generating device that can bereleasably placed in a structure for heating the area within same.

The present invention provides an electrically-operated heat-generatingdevice which can be releasably placed within the structure for thepurposes of heating the area. within the structure. This device can beinstalled simply and easily and can be removed with equal ease andsimplicity. As a result, there is virtually no installation cost, andthe cost of repairs is limited largely to replacement of parts and notto the expenditure of labor. As a result, the overall cost of theelectrically-operated heat-generating device provided by the presentinvention is small. It is therefore an object of the present inventionto provide an electrically-operated heat-generating device which can .bereadily installed within or removed from a structure.

The electrically-operated heat-generating device provided by the presentinvention can be placed on the floor of the structure and suitablyconnected to a source of electric current. Heat is readily transferredto the area above the device and will heat that area. This, in turn,will lead to the heating of the rest of the space within the structure.The electrically-operated heat-generating device is merely laid on thefloor and need not be perma nently associated with that floor.Consequently, the device can be removed readily, either for replacementor for repair. It is therefore an object of the present invention toprovide an electrically-operated heat-generating device that can be laidloosely on the floor of a structure and which can be connected to anoutlet for electric current.

The electrically-operated heat-generating device provided by the presentinvention is made in a number of sections. Each of these sectionscontains a heat-generating element of electrical resistance material andthat element can be connected to a suitable source of electricity. Eachof the sections can be mechanically interlocked into one large overallelectrically-operated heat-generating device. However, by being made insections, the device can be packaged very conveniently and can beassembled into various sizes. In this way, a standard section can beestablished and the interlocking of a number of sections can accommodatestructures of different sizes. The proper selection and interconnectionof the required sections will enable the purchaser to provide fullheating of any given structure. It is therefore an object of the presentinvention to provide a section of an electricallyoperatedheat-generating device which can be connected with other similarsections to assure full heating of a structure.

2,762,896 Patented Sept. 11, 1956 The sections of theelectrically-operated heat-generating device provided by the presentinvention have inter locking surfaces. These surfaces permit readyassembly and disassembly of the sections, and they automatically orientthe sections relative to each other. In this way, the interlockingsurfaces prevent improper assembly of the sections.

The electrically-operated heat-generating device of the presentinvention is equipped with connecting strips which interconnect thevarious sections of the device in parallel. In that way, the varioussections are assured of substantially the same voltage throughout andthe overall heat can be controlled quite readily. The connecting stripis suitably connected to the individual sections by interlockingsurfaces so that the connecting strip will coact with the sections toprovide a suitably integrated electrically-operated heat-generatingdevice. It is therefore an object of the present invention to provideconnecting strips which can be suitably interlocked with the sections ofthe electrically-operated heat-generating device to provide fullelectrical voltage for the resistance elements of the sections.

The various sections of the electrically-operated heatgenerating deviceprovided by the present invention will have the same thickness.Similarly, the connecting strips for the electrically-operatedheat-generating device of the present invention will have the samethickness as do the sections of that device. Consequently, the varioussections can be interlocked together and can be interlocked with theconnecting strips and still provide a uniform flat surface for the usersof the structure. As a part of that fiat uniform surface, there will betabs which are resilient and which can be bent upwardly to facilitatethe interconnection of the electrical components of the sections and ofthe strips. These resilient tabs will then be returned to their normalfiat position where they will overlie those terminals and will completethe plane of the top of the electrically-operated heat-generatingdevice.

Purchasers can select the desired number of sections and those sectionswill be neatly packaged in numbers appropriate to standard sizes ofrooms. Those sections can then be taken to the home or to otherstructures and placed in juxtaposition so that the interlocking surfacesthereof interact to releasably secure the sections together. Thisplacing of the individual sections can be done by unskilled labor.Moreover, these sections need not be cemented to or embedded within thefloor, but need only be placed on the surface of the floor. Theelectrical connections can readily be made by unskilled labor and theresilient tabs which normally overlie those connections can be restoredinto the plane of the upper surface of the electrically-operatedheat-generating device. Once this had been done, a connection can bemade to a suitable source of current and the heat will begin togenerate.

Other and further objects and advantages of the present invention shouldbecome apparent from an examination of the drawing and accompanyingdescription.

In the drawing and accompanying description a preferred embodiment ofthe present invention is shown and described but it is to be understoodthat the drawing and accompanying description are for the purpose ofillustration only and do not limit the invention and that the inventionwill be defined by the appended claims.

In the drawing Fig. l is a plan view, that is partially broken away, ofan integrated electrically-operated heatgenerating device composed of anumber of sections and of a number of connecting strips,

Fig. 2 is a cross sectional view of the electricallyoperatedheat-generating device of Fig. l, and it is taken along the planeindicated by the line 2-2 in Fig. 1,

Fig. 3 is an enlarged plan view of one of the sections of theelectrically-operated heat-generating device of Figs. 1 and 2,

Fig. 4 is an enlarged view of one of the connecting strips of theelectrically-operated heat-generating device of Figs. 1 and 2,

Fig. 5 is an enlarged cross sectional view of a portion of theinterconnecting surfaces of one strip and one section, and

Fig. 6'is an enlarged view in plan of a portion of the connectingsurface of the strip of Fig. 4.

Referring to the drawing in detail, the numeral 10 generally denotes asection of an electrically-operated heatgenerating device that is madein accordance with the principles and teachings of the presentinvention. The section 10 consists of two layers and a heat-generatingelement. The numeral 12 denotes the lower layer of material which formsthe bottom of the section In. This material is intended to resist thepassage of heat through it. Consequently, this material will tend toprevent the loss of heat from the electric heating element to the floorof the structure in which the electrically-operated heatgeneratingdevice is installed. This material should be relatively stiff and rigid,and two such materials that meet these limitations are compositionboards sold under the trade names Masonite and Celotex. Another suchmaterial would be asbestos board. The upper surfaces of the layer 12should be heat reflecting, as by being glazed with a white enamel, alight colored paint or a metallic paint. The combination of theheat-resisting nature of the material itself, together with theheatrefiecting nature of the coating on its upper surface, will enablethe layer 12 to minimize the transfer of heat through it to the floor.

"Disposed on the upper surface of the layer 12 is an elongatedheat-generating element 14 of electric resistance material. The element14 is formed in serpentine fashion so that it covers a considerable areawhile lying flat on the upper surface of the lower layer 12. Thisheatgenerating element 14 will be suitably encased by electricalinsulation of standard and usual type. That insulation will, of course,be designed to resist the heat generated whenever current flows throughthe element 14. Nichrome or other resistance wire can be used for theelement 14.

An upper layer 16 of material is provided to overlie the heat-generatingelement 14; and it is cemented or otherwise secured to the element 14.The layer 16 can be formed with a series of channels to receive andaccommodate the element 14, or that layer can be molded around theheat-generating element 14. This upper layer should be of a materialthat readily transmits heat and which will have a yieldable surface. Onesuch material isrubber that is designed to have a good heat transferringcapacity. Another material is plastic with good heat transferringability. Where the electrically-operated heatgenerating device is to bedisposed beneath a rug or other floor covering, the upper layer 16 canbe of any neutral color and of any smooth appearance. However, where theelectrically-operated heat-generating device is to be exposed, the uppersurface of the layer 16 should be suitably ornamented and colored. Anumber of patterns or designs can be imprinted upon the upper surface ofthe layer 16, and a number of different color schemes can be used. Inthis way, the electrically-operated heat-generating device can be madeattractive and pleasing in appearance.

The ends of the heat-generating element 14 terminate in electricalterminals 18. As indicated particularly in Fig. 5, the terminals 18 havea generally cylindrical portion to receive the ends of theheat-generating element 14 and they have a flat portion with an openingtherethrough'to receive the screw 20. The screws 2% and the terminals 18are of standard form anddesign and can be manipulated readily byunskilled persons.

The section 10 has two generally trapezoidal tongues 22 at one sidethereof. The section 10 also has two generally trapezoidal recesses 24at the opposite side thereof. The tongues 22 and the recesses 24 are inregister with each other, and they interact with the recesses andtongues of other sections 10 and with end sections 11 and 13. The endsections 11 are equipped only with recesses 24, while the end sections13 are equipped only with tongues 22. The particular advantage of theend sections 11 and 13 is that they complete the shape and form of theelectrically-operated heat-generating device and do not leave anyprojections or recesses which could be unsightly. Electrically speaking,the operation of the sections 10, 11 and 13 is identical.

The tongues 22 of one section will fit readily into the recesses 24 ofadjacent sections, and the tongues and re cesses will interact toreleasably lock the sections together. However, forces applied to thetongues 22 or to the areas defining the recesses 24 in a verticaldirection can readily separate the tongues from the recesses. Hence, itis possible to separate one or more sections if replacement or repair isindicated. Moreover, that separation can readily be effected in theevent the user of the structure has to move to still another structure.In this way, ready assembly and disassembly of the sections of theelectrically-operated heat-generating device can be effected.

The numeral 26 denotes a section of a connecting strip. This particularsection is shown as being disposed between two aligned rows of sections10, but if desired a connecting strip could be provided that was usablewith just one row of sections it). Such a connecting strip would bedesirable in a long narrow room or area. The connecting strip 26 isdesirable for a room which is long and wide. The strip 26 has two spacedconductors 28 and 3t), and those conductors are electrically isolatedfrom each other. The section 26 is made of two layers, as indicatedparticularly in Fig. 2. The bottom layer will be generally of the sameheight as the layer 12 of the sections 10 and the upper layer of thestrip 26 will be of the same general thickness as the layer 16 of thesections 10. The overall height of the section 26 will, therefore, besubstantially the same as the overall height of the sections 10.Consequently, the strip 26 will coact with the sections 10 to provide auniform, flat upper surface to the feet of the users of the structure.

Terminals 32 and 34 are provided at the ends of the conductors 28 and 30of the strip 26. These terminals will be of the same type shownparticularly in Fig. 5. As indicated previously, those terminals willhave a cylindrical portion to receive the wire or conductor; and will.

have a. flat, perforated portion to receive the screw 20. Theseterminals 32 and 34 are disposed immediately adacent a recess 36 in oneend of the strip 26. These terminals will coact with terminals on theconnector strip 38 to supply current to the conductors 2% and 30 of theconnector strip 26. The connector strip 38 has two spaced electricalconductors 28 and 30, and those conductors will be appropriatelyconnected to the conductors 28 and 30 of the connector strip 26. Theterminals of theconductors 28 and 30 of the connecting strip 38 will becarried by the tongue 40 of that strip. This tongue will fit within therecess 36 of the connector strip 26 and will releasably maintain the twostrips 26 and 38 in assembled relation. A resilient flap 42 will beprovided on the upper surface of the connector strip 38, and thatresilient flap will overlie the screws 20 and the fiat portions of theterminals carried by the connector strips 26 and 38. The connector strip26 will have a recess to accommodate the resilient flap 42 as well asthe screws 24) and the fiat portions of the terminals of the wires 28and 30 of the connector strips 26 and 38. In this way, aflat uniformsurface is assured for the electricallyoperated heat-generating device,while ready access to the screws and terminals is assured. The connectorstrips 26 and 38 are similar; the principal difference being that st rip26 mustbe connected to the connector strip 38. In

the event t-he electrically-operated heat-generating devicev of thepresent invention was materially longer than indicated in Fig. 1 aswould be the case in anunusually long room, a third type of connectorstrip would beprovided.

That connector strip would have a tongue similar to the tongue 40 of theconnector strip 38 but would have a recess 36 similar to the recess 36of the connector strip 26. By suitable multiplication of the number ofthis third type of strip, the electrically-operated heat-generatingdevice of the present invention can be made to accommodate extremelylong rooms. The conductors 28 and 30 will be of low resistance material,such as copper. Moreover, the cross section of the conductors 28 and 30will be great enough that no appreciable line drop occurs in theoperation of theelectrically-operated heatgenerating device of thepresent invention.

The center strips 26 and 38 have a number of tongues 44 projectingoutwardly from the sides thereof. These tongues are disposed oppositeeach other and extend outwardly from the opposite faces of those strips.These tongues willbe placed in register with similar'recesses 46 in thesections lfl, 11 and 13. The tongues 44 will interact with the recesses46 to releasably lock the sections 10,

. 11 and 13 to the center. strips.26 and 38. The tongues44.and.the.recesses.46 will thus coact with the tongues 22 and. therecesses24 to .provide an integrated, but readily separable, .series ofindividual parts. These individual parts will, when interlocked, asshown in Fig. 1, serve as an integrated unit.

.Theconnecting strips 26 and 38 are equipped with .transversely directedtaps .48. and.50. The taps 48 are .connected to the conductor 28 whilethe taps .50 are connected to the conductor 30. These taps are placed inregister with thetongues44, and they extend into register with, and theyare supported by, .those tongues. The taps 48 and 50 extend parallel toeach other until they reachthe tongues 44 and then. they diverge fromeach other and extend to opposite ends of the tongues 44.

This is desirablesince it minimizes any possibility of the creation ofshort circuits between the terminals of e the taps48 and;50 and of theheat-generating elements- 14. The terminals for the taps 48 are denotedby the numerals 52 and the, terminals for the taps 50 are denoted by thenumerals 54. These terminals will be in register with theterminals ;18of the heat-generating elements 14, and theywill be releasably securedto them by the screws 20.

To connect. the terminals 52 .and 54 with the terminals .18, it is, onlynecessary to remove the screwsZO and to place the terminals 52 or 54 inregister with the terminals 18 and then replace the screws 20. This is asimple process and is one which can be carried out by unskilledindividuals.

.When theterminals .are tobe connected or separated, the resilient flap.56 on the upper surface of the tongues T44.of.the connecting strips 26and 38 will be bent upwardly to expose the screws 20 and the terminals18 and 52 m, 54. .Once the connecting or separating operation has beencompleted, the resilient flaps 56 can be restored tov their normal flatposition. Thus, these flaps 56 will carry ou t th e' plane eifect of theupper surface of the electricallyoper ated, heat-generating device.provided by a the. present invention.

-The sections 10 will be made of a size which is a uniform fractionofstandard areas within homes and other structures. ,For example, inone. preferred embodiment of'the present invention, thesections .10 can.be two feet fourif eet .or can be two feet by six feet. Where thesectionsl were two feet by four feet, it would be possible to: havethose sections heat rooms as small as eight feet by eight feet and toheat rooms that are roughly eight to ,,ten .feetj wide and are oflimitless length. Where the sections are made to be two feet by sixfeet, they can .heat rooms that are from twelve to fourteen feet inwidth than one set of sections in a room, it ispossible to heatextremely largerooms. Moreover, by using connecting strips thatcansupply just one aligned row of sections, it is possible to heatextremely narrow rooms. The length of the room will determine the numberof sections used and will also determine the kind of connecting stripused. In an extremely short room, the connecting strip 38 would bemodifiedby eliminating the tongue 40. In that event, the conductors 28and would terminate short of the upper end of the connecting strip 38.By using various combinations of sections 10, 11 and 13, and byusingvarious combinations of connecting strips 26 and 38, the presentinvention makes it possible to heat rooms of many different sizes andshapes. Moreover, bybeing able. to use several groups ofelectrically-operated heat-generating devices which in turn consist ofsections and connecting strips, the present invention makes it possible.to heat rooms of even great size and area.

In many instances, the electrically-operated heat-generating device. ofthe present invention will not be used as the sole source of heat. Thisis particularly true in old structures where the source of heat isalready installed but is not completely satisfactory. In such cases, theelectrically-operated heat-generating device of the present inventionwillaugment the heat provided by the permanent heating system. Ifdesired, a suitable thermostat can be connected between the conductors28and 30 and a source of current. In other cases, manual control ofthetemperature within the structure can be attained by installing aswitch between the conductors 28 and 30 and the source of current.

- The electrically-operated heat-generating device of the presentinvention is largely free of the objectionable heat lag experienced withmany heating systems. For example, in the case of radiant heatingsystems, the heat must be used to warm the entire floor structure beforethat structure can radiate the heat into the area above it. This oftentimes results in over-shooting? of temperature, and it leads tounpleasant warmth in times of sudden temperature rises of the atmosphereoutside the building. With the electrically-operated heat-generatingdevice of the present invention the response is prompt and it is subjectto very close control.

In some instances the overall dimensions of the integrated sections ofthe electrically-operated heat-generating device will be smaller thanthose of the rug, Where a rug is used, or of the floor where no rug isused. For those instances, filler strips will be provided which willhave the same thickness as the sections, and which can be cut to size.Those filler strips will not have electrical wires embedded within them;and hence they can be cut freely.

Whereas the drawing and accompanying description have shown anddescribed a preferred embodiment of the present invention, it should beapparent to those skilled in the art that various changes may be made inthe form of the invention without aifectinx the scope thereof.

What 1 claim is:

1. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that is releasably disposable onthe floor of a structure to heat the area within said structureimmediately above said floor and that comprises a plurality ofindividual sections of prefabricated unitary construction that areselectively securable to or separable from each other, each of saidsections having a layer of material that is disposable against saidfloor having a heat generating element of electrical resistance materialthat is disposed above said layer, having a layer of material that isdisposed above said heat generating element and that transmits heattherethrough to the area immediately above said floor, and havingterminals for said heat generating element,

fand a plurality of electrical conductors that are wholly external ofsaid sections and'are selectively securable to or separable from theterminals of said plurality of sections and that are selectivelyconnectible to a source of electricity, said plurality of conductorsbeing encased within a prefabricated elongated strip of unitaryconstruction, said strip and said sections being of substantially thesame thickness, said plurality of conductors having taps that areselectively connectible to or separable from said terminals of saidsections, said strip having the exposed surface thereof substantiallycoplanar with the exposed surfacesof said sections.

2. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that is releasably disposable onthe floor of a structure to heat the area within said structureimmediately above said floor and that comprises a plurality ofindividual sections of prefabricated unitary construction that areselectively securable to or separable from each other, each of saidsections having a layer of material that is disposable against saidfioor, having a heat generating element of electrical resistancematerial that is disposed above said layer, having a layer of materialthat is disposed above said heat generating element and that transmitsheat therethrough to the area immediately above said floor, and havingterminals for said heat generating element, and pairs of interactingsurfaces on at least one of said layers of said sections thatselectively maintain said sections in assembled relation, oneinteracting surface of each pair of interacting surfaces being a cutoutin one of said sections and the other interacting surface of said pairof interacting surfaces comprising a tongue with a lateral projection onanother of said sections, said projection lying in back of the portionof said one section that defines said cutout.

3. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that can heat the areaimmediately adjacent said exposed surface and that comprises a pluralityof individual sections of prefabricated unitary construction that lie ina plane and that are selectively securable to or separable from eachother, each of said sections having a heat generating element ofelectrical resistance material and having terminals for said heatgenerating element, and pairs of interacting surfaces on said sectionsthat selectively maintain said sections in assembled relation, oneinteracting surface of each pair of interacting surfaces beingphysically disposed behind the other interacting surface of said pair ofinteracting surfaces so the shear resistance of said sections preventsseparating movement of said sections While said sections lie in saidplane, said one interacting surface of said pair of interacting surfacesbeing a lateral projection on a tongue on one of said sections, saidother interacting surface of said pair of interacting surfaces being theportion of another of said sections that defines a cutout complementaryto said tongue and projection, said sections coacting to provide asubstantially smooth and unbroken heating surface for a structure.

4. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that can heat the areaimmediately adjacent said exposed surface and that comprises a pluralityof individual sections of prefabricated unitary construction that lie ina plane and that are disposable immediately adjacent each other, each ofsaid sections having a heat generating element of electrical resistancematerial and having terminals for said heat generating element, and aplurality of electrical conductors that are wholly external of saidsections and are selectively securable to or separable from theterminals of said plurality of sections and that are selectivelyconnectible to a source of electricity, said plurality of conductorsbeing encased within an elongated strip, and having taps that areselectively connectible to or separable from said terminals of saidsections, said strip lying in said plane and said strip and saidsections being conductors that are wholly external of said sections andare selectively securable to or separable from the terminals of saidplurality of sections and that are selectively connectible to a sourceof electricity, said plurality of conductors being encased within aprefabricated elongated strip of unitary construction, and having tapsthat extend transversely of said strip and are selectively connectibleto or separable from said terminals of said sections, said strip lyingin said plane, said strip and said sections being of substantially thesame thickness, said sections being disposable in side-by-side relationto define a row of aligned sections, said strip being adjacent to andbeing coextensive with one side of said row of aligned sections.

6. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that is releasably disposable onthe floor of a structure to heat the area within said structureimmediately above said floor and that comprises a plurality ofindividual sections of prefabricated unitary construction that lie in aplane and that are selectively securable to or separable from eachother, each of said sections having a heat generating element ofelectrical resistance material and having terminals for said heatgenerating element, and a plurality of electrical conductors that arewholly external of said sections and are selectively securable to orseparable from the terminals of said plurality of sections and that areselectively connectible to a source of electricity, said plurality ofconductors being encased within a prefabricated elongated narrow stripof unitary construction, said electrical conductors having taps that areselectively connectible to or separable from said terminals of saidsections, said taps being encased Within said strip throughout thegreatest portions of their lengths, said sections having flaps overlyingsaid terminals of said heat generating elements to provide access tosaid terminals for the purpose of interconnecting said taps and saidterminals, said strip having the exposed surface thereof substantiallycoplanar with the exposed surfaces of said sections, and pairs ofinteracting surfaces on said sections and strip that selectivelymaintain said sections in assembled relation With each other and withsaid strip, said sections being disposable in side-by-side relation todefine a row of aligned sections, said strip being adjacent to and beingcoextensive with one side of said row of aligned sections, saidheat-generating device being adapted to maintain itself as an integratedunit by the shear resistance of said interacting surfaces and tomaintain itself against sideways dislodgment on said floor bygravity-induced friction.

7. An electrically-operated, heat-generating device that is releasablydisposable on the floor of a structure to heat the area within saidstructure immediately above said floor and that comprises a plurality ofsections that are selectively securable to or separable from each other,each of said sections having a layer of material that is disposableagainst said floor, having a heat generating element of electricalresistance material that is disposed above said layer, having a layer ofmaterial that is disposed above said heat generating element and thattransmits heat therethrough to the area immediately above said floor,and having terminals for said heat generating element, and a pluralityof electrical conductors that are wholly external of said sections andare selectively s'ecurable to or separable from the terminals of saidsections and that are selectively connectible to a source ofelectricity, said plurality of conductors being encased within anelongated strip and having taps extending transversely of said strip,said taps being selectively connectible to or separable from saidterminals of said sections, and interacting surfaces on at least one ofsaid layers of said sections and said strip to selectively hold saidsections in assembled relation with each other and with said strip, saidheat generating device being adapted to maintain itself as an integratedunit by the shear resistance of said interacting surfaces.

8. An electrically-operated, heat-generating device that is releasablydisposable on the floor of a structure to heat the area within saidstructure immediately above said floor and that comprises a plurality ofsections that are selectively securable to or separable from each other,each of said sections having a layer of material that is disposableagainst said floor and that resists the passage of heat therethrough,having a heat generating element of electrical resistance material thatis disposed above said layer of heat resistance material, having a layerof material that is disposed above said heat generating element and thattransmits heat therethrough to the area immediately above said floor,and having terminals for said heat generating element, and a pluralityof electrical conductors that are wholly external of said sections andare selectively securable to or separable from the terminals of saidsections and that are selectively connectible to a source ofelectricity, said plurality of conductors being encased Within anelongated strip and having taps extending transversely of said strip,said taps being selectively connectible to or separable from saidterminals of said sections, and interacting surfaces on at least one ofsaid layers of said sections and said strip to selectively hold saidsections in assembled relation with each other and with said strip, saidtaps being in register with some of said inter-acting surfaces.

9. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that can heat the areaimmediately adjacent said exposed surface and that comprises a pluralityof individual sections of prefabricated unitary construction that lie ina plane and that are selectively securable to or separable from eachother, each of said sections having a heat generating element ofelectrical resistance material and having terminals for said heatgenerating element, and a plurality of electrical conductors that arewholly external of said sections and are selectively securable to orseparable from the terminals of said plurality of sections and that areselectively connectible to a source of electricity, said plurality ofconductors being encased within an elongated strip, and having taps thatare selectively connectible to or separable from said terminals of saidsections, said strip and said sections being of substantially the samethickness, said strip being coextensive with and abutting one edge ofeach of said sections, said taps being encased Within said stripthroughout substantially all of the lengths thereof, said sectionshaving flaps that normally overlie said terminals of said heatingelements but that are movable to expose said terminals for theinterconnecting of said taps and terminals.

10. An electrically-operated, heat-generating device that has asubstantially plane exposed surface and that can heat the areaimmediately adjacent said exposed surface and that comprises a pluralityof individual sections of prefabricated unitary construction that lie ina plane and that are selectively securable to or separable from eachother, each of said sections having a heat generating element ofelectrical resistance material and having terminals for said heatgenerating element, and a plurality of electrical conductors that arewholly external of said sections and are selectively securable to orseparable from the terminals of said plurality of sections and that areselectively connectible to a source of electricity, said plurality ofconductors being encased within an elongated strip, and having taps thatare selectively connectible to or separable from said terminals of saidsections, said strip and said sections being of substantially the samethickness, said strip being coextensive with and abutting one edge ofsaid sections, said taps being encased within said strip throughoutsubstantially all of the lengths thereof, said sections having flapsthat normally overlie said terminals of said heating elements but thatare movable to expose said terminals for the interconnecting of saidtaps and terminals, and pairs of interacting surfaces on said sectionsand strip that selectively maintain said sections in assembled relationwith each other and with said strip, said heat-generating device beingadapted to maintain itself as an integrated unit by the shear resistanceof said interacting surfaces.

References Cited in the file of this patent UNITED STATES PATENTS2,084,468 Wach June 22, 1937 2,110,660 Doczekal Mar. 8, 1938 2,502,148Grothouse Mar. 28, 1950 2,521,540 Richardson Sept. 5, 1950 2,540,465Tice Feb. 6, 1951 2,582,762 Tidd Jan. 15, 1952 2,609,474 Tidd Sept. 2,1952 2,612,585 McCann Sept. 30, 1952 FOREIGN PATENTS 589,752 GreatBritain June 30, 1947

